Wave guide mode converter



Oct. 1 7, 1950 I; H. MEIER I 2,526,383

wAvE GUIDE MODE coNvER'rER Filed Jan. 23, 194e bymm His Attorney.

' Patentedct. 17,

WAVE GUIDE MODE CONVERTER Edwin H. Meier, Tulsa, Okla., assignor to General v Electric Conlpany, a corporation of N ewYork Application January 23, 1948,v Serial No. 4,022

7 3 Claims. (Cl. 178-44) VMy invention relates to a'wave guidestructure and, more particularly, to a Wave guide structure for converting from a rectangular wave guide to a circular wave guide.Y l

. In most systems which employ wave guides to channel the radio frequency energy to and from an antenna, it is often necessary tol change theV position ofthe antenna with respect to theinput guide. Inorder to obtain this `freedom, rotating joints are necessary. That is,l,there must Vbe joints in the radio frequency system where the guide on one sidenof the joint must rotate with respect to the guide on the other side of the joint about the ,y longitudinal axis of the guides.4 order that rotation may take placewithout disturbing the propagationof the radioV frequency power across the point of rotation,` bothA the guide and the mode of propagation must have circular symmetry about the longitudinal axis of the guide in this region. However, most systems employ a rectangular guide propagating the TEM mode. This is especially true where it is necessary to transmit over any appreciable distance. Therefore, some method of conversion from the rectangular TEM mode to asymmetricalY mode in the cylindrical guide is necessary.

It is an object of my invention to convert from va rectangular to a cylindrical wave guide without loss of power. A further object of my invention is joint that is simple and has small losses.

The features of my invention which I believe to be novel, are set forthr with particularity'in the appended claims. My invention itself, however, together with further objects and advantages thereof, may best be understood by reference to the following ldescription taken in conjunction withk the accompanying drawing in which Fig. 1 is a block diagram of a typical rotating coupling section, Fig. 2 is a side view of a wave guide structure embodying my invention, Fig. 3 is an end view of the structure shown in Fig. 2 and Figs. 4 and 5 are cross-sectional views through the guide sections in Fig. 2 conventionally showing the electrical and magnetic vectors for waves therein.

For a better understanding of my invention, now refer to a typical rotating coupling section as shown Vin Fig. 1 in which I have showna rectangular input guide I, and a rectangular output guide 8 which may rotate with respect to the guide I about the axis AA. The rectangular guides'I and 8 are connected to the conversion joints 2 and I respectively. The two cylindrical guides 3 and @extend outwardly from the conversion joints Zand 'I and terminate in the choke joints 4 and 5. `The conversion joint 2 is used to convert from the TEoi mode in the rectangular n guide to a suitable mode in the cylindrical guide.

The .conversion jointl which may be identical in construction` to the joint 2, is used to convert from` the mode in guide li to the TEoi mode in the rectangular guide 8.

At present two types of rotating sections are commonly used.y The rst utilizes the circular f 'IlVlml mode'for `the. cylindrical guides 3 and V6 with 2 and 'i being conversion joints for converting the TEoi .wave Vpropagated in the rec- Y tangular guide to this circular mode in the cylin- `drical guide. lA cylindrical guide which will Y Vpropagate the symmetrical TMm mode will necessarily propagate the circular TEn mode which is Vnonsyrrmietrical about the longitudinal axis ,of

the guide and complicates the design and adjustment of the conversion joints, causing theV distance d in Fig. l to have critical length which itis highly desirable to avoid. The cross section of the cylindrical guide propagating the TMm mode in this case must be relatively large corn-- pared to that of the rectangular guide vwhich causes the conversion joint to be correspondingly large.

A second type or" rotating section now-commonly used as 'the symmetrical portions 3 and comprises sections of coaxial .transmission lines. In this type, the conversion joints- 2 and l comprise `means vfor converting from the TEM wave of the sions'that they propagate waves of the TEn mode.

The choke rotating joints as shown at il and 5 comprise conventional chokes for this type of guide and mode.

. YReferring now to Fig. 2, I have shown a rectangular wave guide section Ill having an inductive diaphragm l I disposed within the section intermediate its ends and having its upper end joining with the circular wave guide section I2. Across a stub end of the guide I2 is connected a short-circuiting plate I3. Attached to the plate vI3 and extending into the guide I2, is a web I4 which is mounted at a 45 degree angle with respect to the longitudinal axis of the rectangular guide, as may be best seen in Fig. 3,

The rectangular wave guide Ill is secured to the side of the cylinder guide I2 with the broad face of the rectangular'guide parallel to the axis y of the cylinder guide. An opening is formed in the wall of the cylinder guide having the same dimensions as the cross section of the end of the rectangular guide. To one side of this' opening the guide extends towards the rotating joint and the converted power is propagated along this leg. To the other side of the opening, the circular guide is short-circuited by plate I3 and the metallic web I I which is supported directly in iront o the plate I3. The Yweb I4 and plate I3 produce two equal electrical vectors, one of which is parallel to the web and the other perpendicular to it. The vector parallel to the web is short-circuited at the leading edge of the web. However, the perpendicular vector is reflected by plate I3 at the end of the stub. If the web IIS is electrically 1/8 guide wave length in length, lthe two equal vectors are perpendicular and have ra phase difference of 90 degrees which results in a 'circular polarized wave being propagated along the cylindrical guide. By using a similar structure at the other end of the system the wave can be fed back into the rectangular guide exactly the same as the one originally supplied. This permits the circular section to be mechanically rotated without affecting the energy supplied tothe output line.

The radio frequency energy is supplied from the rectangular guide into the cylindrical guide lv` with its polarization at an angle of 45 degrees with the plane of the web. This causes two 'components of the 'IEn mode polarized at right angles to one another to be propagated toward the rotating joint. If these two components are equal and 90 degrees out oi time phase, the desired circular polarization is obtained. These conditions are obtained when the distance a in Fig.r2 is equal to 1A; guide wave length and the distance b is equal approximately to 1% guide wave length. Conventional representations of the electrical and magnetic Vectors in the guide sections I9 and I2 are shown in Figs. 4 and 5, for the TEoi and TEn modes respectively.

The inductive diaphragm I I in the rectangular guide near the conversion joint is necessary to match the discontinuity caused by the conversion joint.

With the components of this type Vof rotating section, power may be supplied to either of the rectangular guides and fed from the other rectangular guide into a matched load without any mismatch in the system regardless of the relative position of the two rectangular guides. The chief advantages of my invention are the simplicity of construction, small physical size, absence of excessive voltage gradients, and noncritical length between a pair of conversion joints.

While I have illustrated and described a particular embodiment of my invention, modifications thereoi will occur to those skilled in the art. I desire it to be understood, therefore, that my invention is not to be limited to the particular arrangement disclosed, and I intend in the appended claims to cover all modications which do not depart from the spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. In a wave guide structure, a rectangular section, a circular section, said rectangular section having its major transverse axis parallel to the longitudinal axis of said circular section and its longitudinal axis substantially perpendicular to the longitudinal axis of said circular section, said circular section having a stub end extending at least 1/2 electrical wave length beyond the adjacent wall of said rectangular guide, said stub end terminated by a shorting member, a web member adjacent said shorting member and extending along the longitudinal axis of said circular section for substantially 1/8 electrical wave length and forming an acute angle with the longitudinal axis of said rectangular section, the lengths of said stub and web members and said angle being selected to cause guided waves to be converted from the TEoi mode to the 'IEu mode when passing from said rectangular to said circular section, or from the TEu mode to the TEoi mode when passing in the reverse direction.

2. In a wave guide structure, a rectangular section, a circular section, said rectangular section having its major transverse axis parallel to the longitudinal axis of said circular section and its longitudinal axis substantially perpendicular to the longitudinal axis of said circular section, said circular section having a stub end extending at least 1/Zelectrical wave length beyond the adjacent wall of said rectangular guide and terminated by a shorting member, a web member adjacent said shorting member and extending along Athe longitudinal axis of said circular section forY substantially 1/8 electrical wave length and forming an acute angle with the longitudinal axis Voi'said rectangular section, the lengths of said stub and web members and said angle being selected to cause guided waves to be converted from the TEM mode to the TEu mode.

3. In a wave guide system, a pair of substantially similar relative rotatable wave guide sections, each section having a rectangular section and a circular section, said rectangular section having its major transverse axis parallel to the longitudinal axis of saidrcircular section and its longitudinal axis substantially perpendicular to the longitudinal faxis of said circular section, said circular section having a stub end extending at least 1A? electrical wave length' beyond the adjacent wall of said rectangular guide and terminated by a shorting member, a web member adjacent said shorting ymember and extending along the longitudinal axis of said circular section for substantially 1/8 electrical wave length and forming an acute angle with the longitudinal axis of said rectangular section, thelengths of said stub and web being selected to cause guided waves to be converted from the TEoi mode to the TEM mode, and means for electrically connecting said circular sections so that they are relatively rotatable, transfer of energy between said sec tions being substantially independent of the distance between said rectangular sections. Y

EDWIN H. MEIER.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date y 2,129,669 Bowen Sept. 13, 1938 2,253,503 Bowen Aug. 26, 1941 2,407,267 Ginzton Sept. l0, 1946 2,407,318 Mieher Sept. 10, 1946 2,458,579 Feldman Jan. 11, 1949 OTHER` REFERENCES Radar System Fundamentals TM11-467, published by War Dept., April 28, 1944, pages 194, 195. 

